Trade winds

Trade winds, also called trades are the constant and regular winds that blow in belts on either side of the equator to about 30 degrees north and south over the three oceans that exist at those latitudes. They are caused by air moving in to replace the hot, rising air in the permanent low pressure band at the equator—frequently called the doldrums. They move in south-easterly (northern hemisphere) and north-easterly (southern hemisphere) directions instead of due south or north because of the Earth’s rotation.

Above and below them are belts called the “variables” before bands of prevailing westerlies (called the “Roaring Forties” in the southern hemisphere) occur between about 40 and 60 degrees.

Their existence of all these “belts” has had a profound effect on the history of trade, and European exploration through history:

The British and French used the African route sailing to Australasia, then returned via Cape Horn, making use of the westerlies on both trips.

There have been exceptions. Trade across the north Indian Ocean between India and north-east Africa and the Red Sea made use of the African and Indian monsoons which occurred at different times of the year. Also, currents have been used: as well as the Gulf Stream, the currents running up the west coasts of Africa and South America were a boon to mariners in the age of sail.

The trade winds have always been a moderator of the tropical heat; a blessing to the islands and coasts in their path. John Masefield’s poem "Trade Winds”, later put to music by Frederick Keel, evokes this beautifully:

"In the harbour, in the island, in the Spanish seas,Are the tiny white houses and the orange trees,And day-long, night-long, the cool and pleasant breezeOf the steady Trade Winds blowing.

There is the red wine, the nutty Spanish ale,The shuffle of the dancers, and the old salt's tale,The squeaking fiddle, and the soughing in the sailOf the steady Trade Winds blowing.

And o'nights there's the fire-flies and the yellow moon,And in the ghostly palm trees the sleepy tuneOf the quiet voice calling me, the long low croonOf the steady Trade Winds blowing."